添加优惠券功能，实现价格计算

web/common/types.go

@@ -144,3 +144,37 @@ func (ldt *LocalDateTime) UnmarshalJSON(b []byte) error {
 }
 
 // endregion
+
+// region err
+
+type ServiceErr struct {
+	code int
+	name string
+	msg  string
+}
+
+func (e ServiceErr) Code() int {
+	return e.code
+}
+
+func (e ServiceErr) Name() string {
+	return e.name
+}
+
+func (e ServiceErr) Error() string {
+	return e.msg
+}
+
+func NewErr(name, msg string, code ...int) ServiceErr {
+	_code := 400
+	if len(code) > 0 {
+		_code = code[0]
+	}
+	return ServiceErr{
+		name: name,
+		msg:  msg,
+		code: _code,
+	}
+}
+
+// endregion